An internal combustion engine must receive at least a minimum amount of air flow to operate with stable combustion. This engine operating point may be referred to as a combustion stability limit. The combustion stability limit may be defined in terms of air flow translated into an engine brake torque value. Thus, a minimum engine torque may be specified to ensure stable combustion. This torque value, sometimes referred to as the misfire limit, is the lower bound of the engine torque production.
The engine air intake system may include a throttle valve to regulate the intake airflow and indirectly control the charge (fuel and air) burned in each combustion cycle. The throttle valve position may be electronically controlled by the engine controller in response to various engine and ambient operating conditions. On or more operating parameters, such as fuel injection quantity and timing, may be scheduled and/or adjusted based on the throttle position and corresponding amount of airflow entering the engine. As such, the engine power can be changed depending on the throttle position.
When the engine is operating with a particular throttle position and operating conditions change such that reduced engine torque is requested (e.g. an accelerator pedal tip-out), under some conditions the throttle may remain fixed in position such that the engine generates more torque than requested by the vehicle system controller. In this event, a partial fuel injector cutout may occur to reduce the engine torque to the desired torque target. However, a partial fuel injector cutout may produce undesirable noise, vibration, and harshness (NVH).